It was a bad day for the Bee Gees. Not the day disco died, but Dec. 12, 1992, when the soundtrack to The Bodyguard soared to No. 1, setting it on course to sell 17 million copies and outpace Saturday Night Fever as the best-selling motion picture soundtrack of all time, and to tie the Beatles’ White Album for history’s No. 7 spot.

So what made it so successful, more so than the soundtracks for Purple Rain (which sold 13 million albums), Dirty Dancing (11 million), and even the Celine Dion-floated Titanic (10 million)? For one thing, there was the $121.9 million-grossing movie itself, which starred the still-bankable Kevin Costner as an ex-Secret Service agent and Whitney Houston as an imperiled pop diva.

But the key to the top of the charts was The Bodyguard’s first single, Houston’s schmaltzy update of Dolly Parton’s country ballad ”I Will Always Love You.” However, the song, which hit No. 1 on Billboard’s singles chart just in time for the film’s Nov. 25 opening, almost wasn’t on the album. ”It was originally ‘What Becomes of the Brokenhearted,’ which Kevin Costner picked,” recalls The Bodyguard’s music supervisor, Maureen Crowe. ”But while we were in production, Paul Young covered it for Fried Green Tomatoes.” Enter ”I Will Always Love You,” which had already hit No. 1 on Billboard’s country singles chart twice—in 1974 and 1982.

To be sure, The Bodyguard represents cross-promotion at its cleverest. Houston’s starring role gave her a big-screen platform, and during the film’s 26-week run, moviegoers saw what amounted to an elaborate commercial for the soundtrack.

These days, it seems like every other film has a pop star in it, so it’s tough to imagine a time when movie studios wouldn’t have regarded film/music synergy seriously. Gary LeMel, president of Warner Bros. Worldwide Music, says, ”We had a head of marketing at the time who [said] that music never really helped a film, so when this happened under his watch, it certainly changed his mind. It was a watershed moment.”

Houston had two other hit singles from the triple-Grammy-winning soundtrack—both ”I’m Every Woman” and ”I Have Nothing” went gold—but it was ”I Will Always Love You” that not only supersized album sales and helped trump the Bee Gees; it also dethroned the King, beating out Elvis’ ”Don’t Be Cruel/Hound Dog” for Billboard’s No. 1 single of all time. And though Houston’s record has since been broken four times (the current champion is Mariah Carey/Boyz II Men’s ”One Sweet Day”), The Bodyguard has retained its top-soundtrack title for seven years—and there’s no serious challenger in sight.